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Questions How would a drug that interferes with cross-bridge formation affect muscle contraction?What would you expect to happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to calcium ions?Predict what would happen to a muscle if the motor end plate did not contain acetylcholinesterase. Resting sarcomereADP + P attached to myosin head (stored energy)Step 1Ca+ binds to troponin exposing active site on actinStep 2Myosin head attaches to actinStep 3Pulling of crossbridge towards center of sarcomereADP + P released (energy used)Step 4Myosin head binds another ATPDetachment of cross bridgeStep 5ATP ADP + P, reactivation of myosin head The Contraction Cycle Action potential travels to axon of motor neuronAch is released into synaptic cleftAch diffuses across synaptic cleft & binds to Ach receptors on sarcolemmaThis changes permeability to sodiumSudden rush of sodium into sarcolemmaCauses action potential sarcolemmaAction potential spreads over entire sarcolemma, down t-tubules to cisternaeCisternae release massive amounts of calciumIncrease in calcium – sarcomeres contractAch broken down by AchE Link between NS and muscleMotor neuron – control skeletal muscle fibersSynaptic terminalAcetylcholine (Ach) – chemical released by neuron to communicate with other cellsTriggers change in sarcolemma which triggers contraction Neuromuscular Junction Under control of the nervous system Control of Muscle Fiber Contraction How would severing the tendon attached to a muscle affect the ability of the muscle to move a body part?Why does skeletal muscle appear striated when viewed through a microscope?Where would you expect the greatest concentration of calcium ions in resting skeletal muscles to be? Questions Thintwisted actin moleculesEach has an active site where they interact with myosinResting – active site covered by tropomyosin which is held in place by troponin

ThickMyosinHead attaches to actin during contractionCan only happen if troponin changes position, moving tropomyosin to expose active site Thick and Thin Filaments Smallest functional unit of muscle fiberEach myofibril contains 10,000 sarcomeres end to endInteraction between thick and thin filaments cause contractionBanded appearance Sarcomere Specialized form of SERTubular network around each myofibril